Systems and methods for controlling electrical power systems connected to a power grid

Abstract

A method for controlling an electrical power system connected to a power grid includes receiving a reactive power command and a measured reactive power and generating a reactive power error signal based on a difference between the reactive power command and the measured reactive power. Further, the method includes receiving, via a reactive power regulator, the reactive power error signal. Moreover, the method includes generating, via the reactive power regulator, a voltage command based on the error signal. The method also includes generating, via a droop control, a voltage droop signal. In addition, the method includes generating a voltage error signal as a function of the voltage droop signal and at least one of the voltage command or a measured terminal voltage. Thus, the method further includes generating, via a voltage regulator, a reactive current command based on the voltage error signal.

What is claimed is: 
     
       1. A method for controlling an electrical power system connected to a power grid, the electrical power system having a plurality of clusters of electrical power subsystems, each of the electrical power subsystems defining a generator, a stator power path, and a converter power path for providing power to the power grid, the converter power path having a partial power transformer, the method comprising:
 receiving, via a controller, a reactive power command and a measured reactive power; 
 generating, via the controller, a reactive power error signal based on a difference between the reactive power command and the measured reactive power; 
 receiving, via a reactive power regulator, the reactive power error signal; 
 generating, via the reactive power regulator, a voltage command based on the reactive power error signal; 
 generating, via a droop control, a voltage droop signal; 
 generating, via the controller, a voltage error signal as a function of the voltage droop signal, the voltage command, and a measured terminal voltage, wherein generating the voltage error signal as a function of the voltage droop signal, the voltage command, and the measured terminal voltage further comprises:
 subtracting the measured terminal voltage from the voltage command to obtain a first value, 
 multiplying the measured reactive power by a gain to form the voltage droop signal, wherein the voltage droop signal corresponds with a second value and is configured with a reactive power regulator loop and a voltage regulator loop of the electrical power system; and 
 subtracting the second value from the first value to obtain the voltage error signal; and 
 
 generating, via a voltage regulator, a reactive current command based on the voltage error signal, wherein the reactive current command is obtained by multiplying the voltage error signal by a voltage regulator value. 
 
     
     
       2. The method of  claim 1 , further comprising limiting the voltage command via a first limiter. 
     
     
       3. The method of  claim 1 , wherein generating the reactive current command based on the voltage error signal further comprises:
 generating an output signal based on the voltage error signal; 
 limiting the output signal of the voltage regulator via a second limiter; and, 
 generating the reactive current command based on the limited output signal. 
 
     
     
       4. The method of  claim 1 , wherein the partial power transformer comprises at least one of a two-winding transformer or a three-winding transformer. 
     
     
       5. The method of  claim 1 , wherein the reactive power regulator comprises at least one of a proportional integral (PI) controller, a proportional derivative (PD) controller, a proportional integral derivative (PID) controller, or a state space controller. 
     
     
       6. The method of  claim 1 , wherein the voltage regulator comprises at least one of a proportional integral (PI) controller, a proportional derivative (PD) controller, a proportional integral derivative (PID) controller, or a state space controller. 
     
     
       7. The method of  claim 1 , wherein the generator of each of the electrical power subsystems comprises a doubly-fed induction generator (DFIG). 
     
     
       8. The method of  claim 1 , wherein the electrical power system comprises a wind farm, and wherein the electrical power subsystems comprise wind turbine power systems. 
     
     
       9. A control system for an electrical power system connected to a power grid, the electrical power system having a plurality of clusters of electrical power subsystems, each of the electrical power subsystems defining a stator power path and a converter power path for providing power to the power grid, the converter power path having a partial power transformer, the control system comprising:
 one or more sensors for generating at least one of a measured reactive power or a measured terminal voltage; 
 a controller configured to receive a reactive power command and the measured reactive power and generate a reactive power error signal based on a difference between the reactive power command and the measured reactive power; 
 a reactive power regulator configured to receive the reactive power error signal and generate a voltage command based on the reactive power error signal; 
 a droop control configured to generate a voltage droop signal; 
 the controller further configured to generate a voltage error signal as a function of the voltage droop signal, the voltage command, and the measured terminal voltage, wherein the controller generates the voltage error signal as a function of the voltage droop signal, the voltage command, and the measured terminal voltage by:
 subtracting the measured terminal voltage from the voltage command to obtain a first value, 
 multiplying the measured reactive power by the voltage droop signal to obtain a second value, wherein the voltage drop signal is configured with a reactive power regulator loop and a voltage regulator loop of the electrical power system, and 
 subtracting the second value from the first value to obtain the voltage error signal; and, 
 
 a voltage regulator configured to generate a reactive current command based on the voltage error signal, wherein the reactive current command is obtained by multiplying the voltage error signal by a voltage regulator value. 
 
     
     
       10. The control system of  claim 9 , further comprising a first limiter configured to limit the voltage command. 
     
     
       11. The control system of  claim 9 , wherein the voltage regulator generates the reactive current command based on the voltage error signal by:
 generating an output signal based on the voltage error signal; 
 limiting the output signal of the voltage regulator via a second limiter; and, 
 generating the reactive current command based on the limited output signal. 
 
     
     
       12. The control system of  claim 9 , wherein the partial power transformer comprises at least one of a two-winding transformer or a three-winding transformer. 
     
     
       13. The control system of  claim 9 , wherein the reactive power regulator comprises at least one of a proportional integral (PI) controller, a proportional derivative (PD) controller, a proportional integral derivative (PID) controller, or a state space controller. 
     
     
       14. The control system of  claim 9 , wherein the voltage regulator comprises at least one of a proportional integral (PI) controller, a proportional derivative (PD) controller, a proportional integral derivative (PID) controller, or a state space controller. 
     
     
       15. The control system of  claim 9 , wherein the generator of each of the electrical power subsystems comprises a doubly-fed induction generator (DFIG). 
     
     
       16. The control system of  claim 9 , wherein the electrical power system comprises a wind farm, and wherein the electrical power subsystems comprise wind turbine power systems. 
     
     
       17. A wind farm, comprising:
 a plurality of wind turbine clusters each comprising a plurality of wind turbines, each of the wind turbines having a power converter electrically coupled to a generator with a generator rotor and a generator stator, each of the wind turbines defining a stator power path and a converter power path for providing power to the power grid, the converter power path containing a partial power transformer; 
 a cluster transformer connecting each cluster of wind turbines to a power grid; and, 
 a plurality of turbine controllers, each of the turbine controllers communicatively coupled to one of the wind turbines, the turbine controllers configured to perform one or more operations, the one or more operations comprising: 
 receiving a reactive power command and a measured reactive power; 
 generating a reactive power error signal based on a difference between the reactive power command and the measured reactive power; 
 receiving the reactive power error signal; 
 generating a voltage command based on the reactive power error signal; 
 generating a voltage droop signal; 
 generating, via the controller, a voltage error signal as a function of the voltage droop signal, the voltage command, and a measured terminal voltage, wherein generating the voltage error signal as a function of the voltage droop signal, the voltage command, and the measured terminal voltage further comprises:
 subtracting the measured terminal voltage from the voltage command to obtain a first value, 
 multiplying the measured reactive power by a gain to form the voltage droop signal, wherein the voltage droop signal corresponds with a second value and is configured with a reactive power regulator loop and a voltage regulator loop of the electrical power system; and 
 subtracting the second value from the first value to obtain the voltage error signal; and 
 
 generating a reactive current command based on the voltage error signal, wherein the reactive current command is obtained by multiplying the voltage error signal by a voltage regulator value.